Minhag (Hebrew: מנהג "Custom", pl. minhagim) is an accepted tradition or group of traditions in Judaism. A related concept, Nusach (Hebrew: נוסח), refers to the traditional order and form of the prayers.
Minhag and Jewish law
Halakha (Jewish law) as derived from the Talmud is considered binding upon all Jews. However, in addition to these halakhot, there have always been local customs and prohibitions. Some customs were eventually adopted universally (e.g. wearing a head covering) or almost universally (e.g. monogamy). Others are observed by some major segments of Jewry but not by others (e.g., not eating rice on Passover).
These Minhagim exist in various forms:
Ancient minhagim go back to the time of the Talmud, and are today, generally, regarded as universally binding.
Later minhagim are followed by specific groups.
Jews whose ancestors continued to live in the Middle East and Africa, until the establishment of the State of Israel, regardless of where they live now tend to follow a variety of customs such as Mizrahi-Sephardi or Temani. By like token, Jews whose ancestors lived in Central Europe in the Middle Ages (regardless of where they live now) tend to follow Ashkenazic customs, while those whose ancestors lived in Mediterranean or Asian countries at that time generally follow Sephardic customs. (The Talmud gives detailed rules for people who visit or move to a locale where the custom differs from their own.) Hasidim tend to follow their own Minhagim.
Families and even individuals may adhere to specific minhagim not followed by others.
Discussion in Rabbinic literature
Various sources in Rabbinic literature stress the importance of a long-held tradition, culminating in the statement "the minhag of our fathers is to Torah" (e.g. Tosafot to Menahot 20b s.v. nifsal). Custom can thus determine halachic practice in cases of disagreement among rabbinic authorities. In numerous instances, RabbiMoses Isserles warns that one should not abolish long-held customs. (Isserles' gloss on the Shulkhan Arukh was, in fact, written so as to delineate AshkenaziMinhagim alongside Sephardi practices in one code.)
Despite the above, a minhag does not override clear biblical or talmudic enactments, and one may not transgress the latter for the sake of the former. In fact, any minhag that intrinsically involves an element of halakha violation is considered null and void (see Or Zarua 1:7).
The Talmud (Pesachim 50) rules that a valid minhag accepted by previous generations of a family or community is binding upon all later generations. The Rosh (Makom Shenahagu, 3) states that the Talmud's ruling fundamentally applies to practices undertaken by learned individuals; innovations by the unlearned need only be followed publicly. Other halakhic authorities hold that the Talmud's ruling applies to all valid practices initiated by either learned or unlearned individuals (for discussion of this point see Bach and Beit Yosef to Yoreh Deah 214; Shach, ibid., 214:7).
In most cases, personal acceptance of a new minhag is tantamount to vowing performance of that minhag. Consequently, abandonment of such a minhag typically requires hatarat nedarim or sh'eilat chakham, halakhic procedures for absolving oneself from oaths.
Present day
The acute displacement brought about by World War II and the Holocaust, and the large-scale immigration to the United States, various European countries, and especially the State of Israel, have led to a "liberal mixing" of various minhagim, and arguably the falling into disuse of certain customs. In addition, the baal teshuva movement has created a large group who have no clear tradition from their parents. In response to these phenomena, certain scholars have focused on the minhagim, and attempts have been made to revive minhagim that have fallen into disuse.
Nusach
Both the words nusach and minhag, can also be used for liturgic rite or liturgic tradition; see Different Jewish rites and Popular siddurim under Siddur. In general one must pray according to one's "Nusach of Origin". (Perisha rules that if one abandons a nusach that has been accepted universally by the wider Jewish community, his prayer is disqualified and must be repeated using the accepted nusach (Arba'ah Turim, Orach Chayim, 120 ad loc).
"Nusach", although usually used as above, also has implications as regards "community minhagim" in general; the main segments of traditional Judaism, as differentiated in terms of Nusach (broadly and narrowly) are:
Minhag Sefarad: in general refers to the various Sephardi liturgies, but also to obligation/permissibility of Kabbalistic elements within the rite.
"Ta'amei HaMinhagim", Rabbi A. I. Sperling, 1896; translation: "Reasons for Jewish customs and traditions". Bloch Pub. Co 1968. ISBN 081970184X
"Likutei Maharich". Rabbi Yisroel Chaim Freedman of Rachov.
"Sefer HaMinhagim", Rabbis M. Greenglass and Y. Groner, 1966; translation: “The Book of Chabad-Lubavitch Customs”. Sichos In English Pub. 1998. ISBN 0826605559 *
"Otzar Ta'amei ha-Minhagim", Rabbi Shmuel Gelbard, 1995; translation: "Rite and Reason" Feldheim Pub. 1997 ISBN 0873068890
General
"The Minhagim: The Customs and Ceremonies of Judaism, Their Origins and Rationale", Rabbi Abraham Chill. Sepher Hermon 1978. ISBN 0872030776
"The Biblical and Historical Background of Jewish Customs and Ceremonies", Rabbi Abraham Bloch. Ktav 1978. ISBN 0870683381
"Jewish Book of Why", Rabbi Alfred Kolatch. Jonathan David 1995. ISBN 0824603141
"To Be a Jew: A Guide to Jewish Observance in Contemporary Life", Rabbi Hayim Donin. Basic Books 1991. ISBN 0465086322
"The Complete Book of Jewish Observance", Rabbi Leo Trepp. Behrman House Publishing 1980. ISBN 0671417975
"Minhagei Yisrael: Origins and History", Rabbi Daniel Sperber. Mossad Harav Kook, 1998.
"Minhag".
